Jupiter's Great Red Spot -- a massive storm larger than Earth that resembles a hurricane -- has shrunk to its smallest size ever measured, according to NASA.

In the late 1800s the red spot was an oval 25,500 miles wide. Now it's a circle that's 10,250 miles across.

The diameter of the Earth is roughly 8,000 miles.

The storm has been raging for at least hundreds of years, NASA reports. It may have been first spotted as early as the 1660s, though the earliest known drawing of the spot was made in the 1830s.

Beginning in 2012, amateur observations revealed a noticeable increase in the rate at which the spot is shrinking -- by 580 miles per year -- changing its shape from an oval to a circle.

"In our new observations it is apparent very small eddies are feeding into the storm," said Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "We hypothesized these may be responsible for the accelerated change by altering the internal dynamics and energy of the Great Red Spot," she said.

Simon's team will continue to study the storm to determine whether the eddies can feed or sap momentum entering the spot, resulting in this yet unexplained shrinkage.